![\"Shared](\"https:\/\/www.techdesignforums.com\/practicefiles\/2013\/10\/tdf-ment-3dpowergrid-fig1lg.jpg\")
<\/a><\/div>Figure 1 <\/span>Shared power supplies between dies A, B, and C<\/p><\/div>\n The presence of multiple die also highlights the need for 2.5D\/3D PGA solutions to support heterogeneous technology nodes. Each die in a system may have be designed on a different process, as dictated by node maturity for the applications it contains. So, a system could contain die designed at 40nm and 28nm, and an interposer designed at 65nm.<\/p>\n Enabling incremental technology file definition and calibration is also a plus. End users then need only calibrate the new part of a stack definition related to the 2.5D\/3D integration, rather than re-calibrate the IC portion of a stack definition.<\/p>\n Then there is the question of how everything within a system is mounted and connected. Figure 2 shows how 2.5D\/3D flows must take account of the specific \u2018objects\u2019 required for vertical integration. These can include backside bumps and backside metal layers.<\/p>\n The latter is a good illustration of the type of challenge these present for PGA software: The backside metal layers in a 3D structure are routed at 45 degree angles instead of the usual 90 degrees used for front-side metal layers.<\/p>\n For 3D, there is then the further need to support the use of through-silicon vias (TSVs) between front and backside metals. Meanwhile for 2.5D systems, PGA tools must be able to handle passive interposers that contain only metal (no devices underneath).<\/p>\n Figure 2 <\/span>2.5D\/3D-specific 'objects'<\/p><\/div>\n Due to the typical size of 2.5D and 3D systems, and the additional complexity introduced by the possible need to integrate third-party die, PGA solutions must be capable of running in three different modes.<\/p>\n Power model-based PGA is already implemented in existing solutions. Each of the die is represented by its compact power model, and the PGA software analyzes the full 2.5D\/3D IC system using those models and their connections. This mode can be run fairly quickly to provide a high-level PGA of the system, though the only issues that it detects are related to inter-die connections.<\/p>\n Only one additional degree of complexity must be considered when running a power model-based PGA on a system incorporating multiple technology nodes. Power models are generated for technology node-specific corners, so PGA solutions here must be able to handle multi-die systems represented by compact power models generated for different corners. For instance, one 90nm die model is generated for a 1.2V corner, while a 65nm die model is generated for a 1.0V corner.<\/p>\n This mode is not covered by existing PGA solutions and is also computationally expensive.<\/p>\n End users want to analyze the voltage drop on specific multi-die nets similar to those shown in Figure 1. However, to provide such visibility, the software\u2019s capacity and turnaround time must be several orders of magnitude greater than seen in PGA solutions already on the market.<\/p>\n The hybrid solution is induced by 2.5D\/3D third-party die integration. It can handle a mix of compact power models and dies (Figure 3). In a given system, a third-party die is only represented by its compact model for integration into the system PGA.<\/p>\nHeterogeneous nodes<\/h3>\n
2.5D and 3D integration \u2018objects\u2019<\/h3>\n
<\/a><\/div>Use models<\/h2>\n
1. Power model-based power grid analysis<\/h3>\n
2. Full 2.5D\/3D power grid analysis<\/h3>\n
3. Hybrid power grid analysis<\/h3>\n